The claims of the above applications and patents are concerned, primarily, with solids adherence problems related to the heating and evaporating of aqueous solutions wherein minerals are precipitated and from scale on contacting surfaces. Such adherence problems, as taught in the above applications and patents, are eliminated by use of oil films on preferentially oil wettable surfaces that are substantially zero water adsorbent such as provided by the fluorocarbon polymers. The research pertaining to the above four applications, while directed generally to heat exchange, concerned itself primarily with heating and evaporating mineralized aqueous solutions. Since that time I have more specifically directed my research to the extraction of heat from geothermal fluids by cooling with a circulating coolant and have found the problem and its solution to be similar to those involved in the heating and evaporating systems, with some important exceptions. In both situations oil films on substantially zero water adsorbent surfaces are required to prevent adherence of solids, and fluorocarbon polymers, particularly FEP, appear to be the most suitable materials for this purpose. I have also tested parylene materials, specifically Union Carbide's Parylene-N and Parylene-C which, too, are substantially zero water adsorbent and do not scale up, but which also do not stay well bonded to the metal surfaces, especially in systems where steam vapor is being condensed. Parylene is defined in Reinhold, The Condensed Chemical Dictionary, Eighth Edition .COPYRGT. 1971, page 660 as follows:
Parylene -- Generic name for thermoplastic film polymers based on para-zylylene and made by vapor-phase polymerization.
Fep films heat bonded to metal surfaces, in contrast to heating and evaporation systems, will not stay bonded, but tend to form water blisters of pure water beneath the film, pulling the film from the metal surface in systems where water vapor is being condensed, whereas in heating and evaporating systems such FEP films, heat bonded to the metal, remained perfectly intact after many hours of exposure. The only heat bondable fluorocarbon polymer material I have found suitable for condensing steam systems, and one that appears to remain bonded indefinitely, is FEP applied, not as a film, but as a dispersion from a distilled water dispersion or applied as a finely divided particle coating, by static charge dry spraying, then heat bonded to the surface in a conventional oven. Such FEP dispersions are known in the art and a suitable dispersion is known as DuPont FEP dispersion. My explanation of this unusual phenomenon is simply that the dispersion appears to be bonded as individual particles, not actually forming a continuous film and is therefore more porous, permitting steam to penetrate to the condensing metal surface, form water and ooze back through the pores of the FEP coating, whereas with bonded FEP film, the steam penetrates through the smaller pores to the metal wall, condenses, but cannot return through the smaller pores, thereby pushing the continuous film from the metal surface to which it was originally heat bonded. This becomes vital to heat exchange systems as disclosed in this application, as the FEP dispersion is the only material I have found thus far to provide a relatively permanently heat bonded, substantially zero water adsorbent fluorocarbon polymer for prevention of solids adherence when coated with an oil film, when cooling or condensing water vapor as distinguished from evaporating processes. In my work with cooling geothermal brines in the Imperial Valley of California, I found that all of the interiors of the cooling heat exchanger should be coated with such a substantially zero water adsorbent coating, including both the heat transfer tube itself and the interior of the heat exchanger shell. I ran tests using FEP coated heat transfer tubes, but with epoxy coating on the shell interior, as set forth in my U.S. Pat. No. 2,903,243 dated Sept. 8, 1959, Col. 3, line 5, in claim 3 of said patent finding that the FEP coated tube did not scale, but that the epoxy coating scaled immediately, soon having lost its ability to stay wet with oil because it is water adsorbable and soon becomes water wettable. Many technical experts have seen my test system, and admit to its beneficial effects and readily agree that it may well prove to be the most practical solution to the nearly impossible scaling condition involved with cooling and extraction of useful energy from geothermal fluids.
In the present specification and claims reference is made to an "immiscible liquid" or "oil," which is temporarily intimately mixed or dispersed, as by agitation, pressure or the like with an aqueous solution to be heated to remove impurities therefrom. Such immiscible liquid or oil while preferably a hydrocarbon need not necessarily be true hydrocarbon but may be any liquid preferably organic which is immiscible with the aqueous liquid containing impurities to be removed. The particular immiscible liquid or oil to be employed depends on the aqueous liquid to be treated though there may be wide variations dependent on the availability of the liquid and the particular conditions under which the process is to be carried out. For example in treating brine, I have found mineral oils such as automobile lubricating oils, turbine oils and the like to be particularly satisfactory and these have actually been used in the process herein described. The turbine oils have been found to be stable and not readily oxidizable on heating. For refining vegetable materials such as beet sugar solutions or the like a non-toxic mineral or vegetable oil may be used. Where a high degree of heat stability is required a heat resistant oil such as silicone fluids or silanes may be employed and are contemplated as intended to be included under the terms "immiscible liquid" and "oil" as used in the present specification and claims, as set forth in my U.S. Pat. No. 3,891,496, Col. 14, beginning line 12.
The "oil" or "immiscible liquid" should be of different specific gravity and of higher boiling point than the aqueous solution with which it is to be temporarily mixed. Mineral oils, vegetable oils, silicone fluids and silanes are well known products and are defined for example in Reinhold's The Condensed Chemical Dictionary, sixth Edition.
It will be understood that by the term "immiscible" as used in the present specification and claims a permanent mixture is referred to since the immiscible liquid or oil on the one hand and the aqueous solution on the other hand cannot be permanently mixed but one may be temporarily mixed or dispersed in the other as by the aid of pressure, agitation or the like and such temporary mixture or dispersion may thereafter be separated by suitable means as is well known in the art.